The UltraSPARC IV processor is derived from Sun Microsystems high-end UltraSPARC III processor, providing the same fundamental features, and offering the advantage of high throughput utilizing Chip Multithreading (CMT) technology. The UltraSPARC IV processor features two cores, each based on the UltraSPARC III processor. From the software perspective, the UltraSPARC IV processor appears as two software-visible logical processors.In common with all other members of the UltraSPARC III processor family, the UltraSPARC IV processor is a 4-way superscalar processor, meaning it attempts to fetch 4 instructions at a time from the L1 instruction cache, and (given the appropriate instruction mix) is capable of sustaining an execution rate of 4 instructions per clock cycle. Each instruction is processed through a 14-stage pipeline that starts with address generation and ends with the final retirement of any valid execution result. A 16-entry instruction queue decouples instruction fetch from instruction issue, working to buffer any discrepancies 1-2 between these two rates. Thus, if more instructions are fetched than can be issued repeatedly, an empty instruction queue gradually will fill. Or, if the next instruction fetch misses in the L1 cache, a filled instruction queue can hide this break in the flow of instructions through the pipeline, by continuing to supply the execution units with instructions for the several clock cycles needed to retrieve the missing block of instructions from the integrated L2 cache.To enhance throughput, while instructions enter and exit the instruction queue in strict program order, they can complete executing out-of-order. For example, if a short latency instruction follows a long latency instruction in the pipeline, the fast operation does not need to wait on the slow one to finish. Instructions fetched together will enter the queue in parallel, but, within the constraints imposed by program order, they may exit the queue in company with instructions fetched either earlier or later (depending on the specific instruction mix and availability of the necessary functional units).The UltraSPARC IV processor is supported by Sun's popular Solaris operating system, providing access to the more than eight thousand applications that have been developed for the SPARC/Solaris platform over the years. Comprehensive sets of programs are available for many fields, including engineering, manufacturing, telecommunications, financial services, health, retail, ecommerce, and a variety of other industry segments.